Air-bearing chuck

ABSTRACT

An air-bearing chuck includes a nozzle portion and a gas channel portion. The nozzle portion is provided with a plurality of support force nozzles for generating an air cushion on a top surface of the nozzle portion. The gas channel portion includes a first gas channel configured to transmit a first gas to the plurality of support force nozzles to provide support force. Embodiments of the present application can implement that the first gas channel transmits the first gas to the plurality of support force nozzles to provide support force, and an air cushion is generated on the top surface of the nozzle portion by regulating gas flow of the first gas in the first gas channel, thereby keeping a supported object supported by the air cushion stably floating up on one side, away from the top surface of the nozzle portion, of the air cushion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of InternationalApplication No. PCT/US2020/049009 filed on Sep. 2, 2020, which claimspriority to U.S. 62/953,696 filed on Dec. 26, 2019. And this applicationalso claims priority to Chinese patent applications No. 202011569044.8filed on Dec. 25, 2020, and No. 202023200409.8 filed on Dec. 25, 2020.These applications are incorporated herein by reference in theirentireties.

TECHNICAL FIELD

The present application relates to the technical field of chuckstructure design, and in particular to an air-bearing chuck.

BACKGROUND

A wafer is usually fixed on a chuck in a clamping manner duringpreparation, measurement or the like of the wafer. However, whenclamping force is relatively large, an original shape of the wafer iseasily changed. In addition, debris particles or other contaminants areeasily introduced on the wafer because it is difficult to guaranteecleanliness of a clamping tool, therefore measurement errors are causedto the original shape of the wafer.

SUMMARY

In view of this, embodiments of the present application provide anair-bearing chuck, to implement that an air cushion is generated on atop surface of a nozzle portion, so as to keep a supported object suchas a wafer supported by the air cushion stably floating up on one side,away from the top surface of the nozzle portion, of the air cushion,thereby avoiding measurement errors caused by a clamping tool to anoriginal shape of the wafer.

An embodiment of the present application provides an air-bearing chuck.The air-bearing chuck includes: a nozzle portion, provided with aplurality of support force nozzles for generating an air cushion on atop surface of the nozzle portion; and a gas channel portion, includinga first gas channel configured to transmit a first gas to the pluralityof support force nozzles to provide support force.

In an embodiment of the present application, the nozzle portion furtherincludes a plurality of openings, and the plurality of openings arearranged alternately with the plurality of support force nozzles.

In an embodiment of the present application, the plurality of supportforce nozzles and the plurality of openings are arranged in anaxisymmetric pattern on the top surface of the nozzle portion.

In an embodiment of the present application, the plurality of supportforce nozzles and the plurality of openings are arranged in a pluralityof concentric nozzle rings equally spaced at an interval of ΔR.

In an embodiment of the present application, a radius of a nozzle ring,farthest from the center of the air-bearing chuck, of the plurality ofconcentric nozzle rings is 0 mm-20 mm smaller than a radius of theair-bearing chuck.

In an embodiment of the present application, each support force nozzleand an adjacent opening that are on any one of the plurality ofconcentric nozzle rings are tangentially spaced at a constant distanceΔT.

In an embodiment of the present application, as a distance between pernozzle ring of the plurality of concentric nozzle rings and the centerof the air-bearing chuck increases, a total number of nozzles on pernozzle ring increases in an even number, and the even number includesany one of 2, 4, 6, 8 and 10.

In an embodiment of the present application, a difference between ΔR andΔT is less than 5 mm.

In an embodiment of the present application, the plurality of openingsinclude a plurality of suction force nozzles. The gas channel portionfurther includes a second gas channel, and the second gas channel isconfigured to transmit a second gas to the plurality of suction forcenozzles to provide suction force.

In an embodiment of the present application, a plurality of first gasthrough holes corresponding to the plurality of support force nozzlesare disposed on both the nozzle portion and the gas channel portion, anda plurality of second gas through holes corresponding to the pluralityof openings are disposed on both the nozzle portion and the gas channelportion. The first gas channel is connected to the plurality of supportforce nozzles through the plurality of first gas through holes, and thesecond gas channel is connected to the plurality of openings through theplurality of second gas through holes.

In an embodiment of the present application, the first gas channelincludes a first annular channel and a plurality of first channelsconnected to the first annular channel, and the second gas channelincludes a second annular channel and a plurality of second channelsconnected to the second annular channel.

In an embodiment of the present application, the gas channel portionincludes a first gas layer and a second gas layer that are stacked. Thefirst gas channel is located in the first gas layer, and the second gaschannel is located in the second gas layer.

In an embodiment of the present application, the first gas layer isprovided with a first groove for accommodating the first gas channel,and the second gas layer is provided with a second groove foraccommodating the second gas channel.

In an embodiment of the present application, the air-bearing chuckfurther includes an air pressure regulator. The air pressure regulatoris configured to regulate a flow rate of a gas in each of the first gaschannel and the second gas channel to hold a wafer at a predetermineddistance from the top surface of the nozzle portion, so as to measure ageometry of the wafer, and the geometry of the wafer includes one ormore of a flatness and a shape of the wafer.

In an embodiment of the present application, the air-bearing chuckfurther includes a controller. The controller is configured to controlthe air pressure regulator to regulate the flow rate of the gas in eachof the first gas channel and the second gas channel to hold the wafer atthe predetermined distance from the top surface of the nozzle portion,so as to measure the geometry of the wafer.

In an embodiment of the present application, the predetermined distanceranges from 0 μm to 50 μm when the air-bearing chuck is configured tomeasure the flatness of the wafer.

In an embodiment of the present application, the predetermined distanceranges from 60 μm to 1500 μm when the air-bearing chuck is configured tomeasure the shape of the wafer.

In an embodiment of the present application, the plurality of openingsinclude a plurality of flow guide holes. The plurality of flow guideholes are configured to guide the first gas ejected from the pluralityof support force nozzles to flow back to the nozzle portion when thefirst gas encounters a to-be-measured object. The gas channel portionfurther includes a third gas channel, and the third gas channel isconfigured to make the first gas that has flowed back to the nozzleportion flow out of the air-bearing chuck.

In an embodiment of the present application, the air-bearing chuck has amirror polished surface higher than or equal to level N4 in accordancewith an ISO standard.

In an embodiment of the present application, a material of the nozzleportion includes any one of aluminum, glass, microcrystalline siliconand ceramic. The material is configured to be mirror polished. The topsurface, obtained after being polished, of the nozzle portion issufficiently flat, so that interference fringes are shown on the topsurface of the nozzle portion.

According to technical solutions provided in the embodiments of thepresent application, a plurality of support force nozzles are arrangedon an air-bearing chuck, and an air cushion is generated on a topsurface of a nozzle portion, so as to keep a supported object such as awafer supported by the air cushion stably floating up on one side, awayfrom the top surface of the nozzle portion, of the air cushion. Sincethere is no need to use a clamping tool to clamp the wafer duringmeasurement, a shape of the wafer is not affected, thus reducing errorsduring measurement of the wafer.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1a is a schematic structural diagram of an air-bearing chuckaccording to an embodiment of the present application.

FIG. 1b and FIG. 1c are schematic top views of the air-bearing chuck inFIG. 1 a.

FIG. 2a is a schematic structural diagram of an air-bearing chuckaccording to another embodiment of the present application.

FIG. 2b to FIG. 2k are schematic top views of an air-bearing chuck.

FIG. 3a is a schematic top view of the first gas channel in FIG. 2 b.

FIG. 3b is a schematic top view of the second gas channel in FIG. 2 b.

FIG. 4a is a schematic top view of the first gas channel in FIG. 2 e.

FIG. 4b is a schematic top view of the second gas channel in FIG. 2 e.

FIG. 5 is a schematic structural diagram of an air-bearing chuckaccording to another embodiment of the present application.

FIG. 6 is a schematic structural diagram of an air-bearing chuckaccording to still another embodiment of the present application.

FIG. 7 is a schematic structural diagram of an air-bearing chuckaccording to yet another embodiment of the present application.

FIG. 8a and FIG. 8b show an exemplary air-bearing chuck with vacuumnozzles and pressure nozzles for holding a wafer on an air cushion.

FIG. 8c is a schematic diagram of connection layers of pressure nozzlesand vacuum nozzles of an air-bearing chuck.

FIG. 8d is a schematic side view of a stacked structure of anair-bearing chuck according to an embodiment of the present application.

FIG. 8e is a schematic side view of a stacked structure of anair-bearing chuck according to another embodiment of the presentapplication.

FIG. 8f shows a top surface of a top plate of the stacked structure inFIG. 8 e.

FIG. 8g shows a bottom surface of a top plate of the stacked structurein FIG. 8 e.

FIG. 8h is a top view of an exemplary manifold plate of the stackedstructure in FIG. 8 e.

FIG. 8i is a bottom view of an exemplary manifold plate of the stackedstructure in FIG. 8 e.

FIG. 8j is a top view of a back cover plate of the stacked structure inFIG. 8 e.

FIG. 8k is a bottom view of a back cover plate of the stacked structurein FIG. 8 e.

FIG. 9a and FIG. 9b are schematic structural diagrams of an exemplarymanifold chamber according to an embodiment of the present application.

FIG. 10a is a schematic structural diagram of a dual Fizeauinterferometer-based tool.

FIG. 10b is a schematic structural diagram of a shearinginterferometer-based tool.

FIG. 10c is a schematic structural diagram of an architecture formeasuring a wafer geometry.

FIG. 10d is a schematic diagram showing positions of a position sensorand a capacitive sensor relative to a wafer.

FIG. 10e is a schematic diagram of calibration of a position sensor.

FIG. 10f is a schematic diagram of a relationship between a positionsensor reading Vx and a capacitive sensor reading CPn during calibrationof a position sensor.

FIG. 11a and FIG. 11b are schematic diagrams of performing a measuringmethod of a wafer flatness TTV by utilizing the architecture shown inFIG. 10 c.

FIG. 12a and FIG. 12b are schematic diagrams of performing a measuringmethod of a wafer shape by utilizing the architecture shown in FIG. 10c.

FIG. 13 is a schematic diagram illustrating that a wafer in a verticalposition is prone to shape change when tilted.

FIG. 14 is a schematic structural diagram of an exemplary goniometer formeasuring a patterned wafer tilt platform according to an embodiment ofthe present application.

FIG. 15a is a schematic diagram of a chuck mark or artifact occurredwhen a wafer is vacuum down on a vacuum chuck.

FIG. 15b is a schematic diagram of a wafer floating up on an air-bearingchuck.

FIG. 16a to FIG. 16c are schematic diagrams of a method fordifferentiating between real features and chuck marks or artifacts on awafer surface.

DESCRIPTION OF EMBODIMENTS

The following clearly and completely describes the technical solutionsin the embodiments of the present application with reference to theaccompanying drawings required to be used in the embodiments of thepresent application. Apparently, the following descriptions of theaccompanying drawings are merely some but not all of the embodiments ofthe present application.

It should be noted that all related embodiments obtained by a person ofordinary skill in the art based on the embodiments of the presentapplication without creative efforts shall fall within the protectionscope of the present application.

In the embodiments of the present application, an air-bearing chuck isprovided, which is described in detail below.

It should be understood that, the air-bearing chuck in the embodimentsof the present application may be configured to support a supportedobject such as a wafer, and may be applied to the field of wafergeometry measurement, semiconductor manufacturing, or the like. Theapplication fields of the air-bearing chuck are not specifically limitedin the embodiments of the present application. A top surface of a nozzleportion of the air-bearing chuck may be in a circular, rectangular,square, or another regular or irregular shape. The shape of the topsurface of the nozzle portion is not specifically limited in theembodiments of the present application.

FIG. 1a is a schematic structural diagram of an air-bearing chuckaccording to an embodiment of the present application. FIG. 1b and FIG.1c are schematic top views of the air-bearing chuck 100 in FIG. 1 a.Referring to FIG. 1a to FIG. 1 c, the air-bearing chuck 100 includes anozzle portion 110 and a gas channel portion 120. The nozzle portion 110includes a plurality of support force nozzles 111, and the plurality ofsupport force nozzles 111 are configured for generating an air cushion10 on a top surface 1 of the nozzle portion 110. The gas channel portion120 includes a first gas channel 121 configured to transmit a first gasto the plurality of support force nozzles 111 to provide support force.

It should be understood that, the plurality of support force nozzles 111may be arranged on a plurality of concentric rings (as shown in FIG. 1b) surrounding the center of the nozzle portion 110, and each concentricring may be provided with one or more support force nozzles 111; or theplurality of support force nozzles 111 may also be arranged on aplurality of parallel lines (as shown in FIG. 1c ); or the plurality ofsupport force nozzles 111 may also be arranged on a plurality of radiiextending from the center of the nozzle portion 110 all the way out, aslong as the air cushion 10 may be generated on the top surface 1 of thenozzle portion 110. The arrangement manner of the plurality of supportforce nozzles 111 is not specifically limited in the embodiment of thepresent application. The plurality of support force nozzles 111 may bein any regular or irregular shape such as a circular, triangular,elliptical, annular, or the like, which is not specifically limited inthe embodiment of the present application. In addition, the air cushion10 may be generated by a gas ejected from the plurality of support forcenozzles 111. The air cushion 10 is configured to keep a supported objectsuch as a wafer floating up on one side, away from the top surface 1 ofthe nozzle portion 110, of the air cushion 10. The plurality of supportforce nozzles 111 may be spread over the entire top surface 1 of thenozzle portion 110 to equalize support force received by the supportedobject such as a wafer that is supported by the air cushion 10, therebyfacilitating maintaining an original shape of the wafer, and accuratelymeasuring a geometry of the supported object when the supported objectis in a floating state.

According to the technical solution provided in the embodiment of thepresent application, a plurality of support force nozzles are disposedon a nozzle portion of an air-bearing chuck, and a first gas channel fortransmitting a first gas to the plurality of support force nozzles toprovide support force is disposed on a gas channel portion of theair-bearing chuck, so that the first gas is transmitted to the pluralityof support force nozzles through the first gas channel to providesupport force, and an air cushion is generated on a top surface of thenozzle portion by utilizing the support force, thereby keeping asupported object such as a wafer supported by the air cushion stablyfloating up on one side, away from the top surface of the nozzleportion, of the air cushion. Since there is no need to use a clampingtool to clamp the wafer during geometry measurement, and a shape of thewafer is not affected, errors during measurement of the wafer arereduced.

FIG. 2a is a schematic structural diagram of an air-bearing chuck 200according to another embodiment of the present application. Theembodiment illustrated in FIG. 2a is a modified example of theembodiment illustrated in FIG. 1a . FIG. 2b to FIG. 2k are schematic topviews of an air-bearing chuck 200 according to some embodiments of thepresent application. Referring to FIG. 2a to FIG. 2 k, a differencebetween the two embodiments lies in that, in the embodiment illustratedin FIG. 2a to FIG. 2 k, the nozzle portion 110 further includes aplurality of openings 112, and the plurality of openings 112 arearranged alternately with the plurality of support force nozzles 111.

It should be understood that, the plurality of support force nozzles 111and the plurality of openings 112 that are alternately arranged may bearranged in a non-axisymmetric manner (as shown in FIG. 2b ), or may bearranged in an axisymmetric manner (as shown in FIG. 2c to FIG. 2g ).The plurality of support force nozzles 111 and the plurality of openings112 that are alternately arranged may be arranged in a plurality ofconcentric nozzle rings such as concentric rings (as shown in FIG. 2 e,FIG. 2 g, FIG. 2 h, and FIG. 2k ), concentric polygons such as pentagons(as shown in FIG. 2f ), and the like; or may be arranged on a pluralityof parallel lines (as shown in FIG. 2b to FIG. 2 d, and FIG. 2i to FIG.2j ); or may be arranged in another regular or irregular pattern. Theplurality of support force nozzles 111 and the plurality of openings 112that are alternately arranged may be arranged on a same nozzle ring ofconcentric nozzle rings or a same parallel line with a single supportforce nozzle 111 and a single opening 112 as repeating units (as shownin FIG. 2d to FIG. 2f ); or may be arranged on a same nozzle ring or asame parallel line with a plurality of support force nozzles 111 or aplurality of openings 112 arranged on the nozzle ring (as shown in FIG.2g ) or the parallel line (as shown in FIG. 2c ); or may be arranged ona same parallel line with a single support force nozzle 111 and aplurality of openings 112 as repeating units or with a plurality ofsupport force nozzles 111 and a single opening 112 as repeating units(as shown in FIG. 2b ). As for the plurality of support force nozzles111 and the plurality of openings 112 that are alternately, totalnumbers of support force nozzles 111 and openings 112 (e.g., suctionforce nozzles) on every two adjacent nozzle rings of concentric nozzlerings may be the same (as shown in FIG. 2f ), or may be different (asshown in FIG. 2e and FIG. 2g ); and total numbers of support forcenozzles 111 and openings 112 on every two adjacent parallel lines of aplurality of parallel lines may be the same (as shown in FIG. 2d ), ormay be different (as shown in FIG. 2b and FIG. 2c ), as long as the aircushion may be generated on the top surface of the nozzle portion 110.The arrangement manner of the plurality of support force nozzles 111 andthe plurality of openings 112 that are alternately arranged is notspecifically limited in the embodiment of the present application. Anumber of the plurality of support force nozzles 111 may be the same asthat of the plurality of openings 112 (as shown in FIG. 2h and FIG. 2i), or may be different from that of the plurality of openings 112 (asshown in FIG. 2i and FIG. 2k ).

It should also be understood that, one or more of the plurality ofsupport force nozzles 111 and the plurality of openings 112 may be in acircular (as shown in FIG. 2b as well as FIG. 2e to FIG. 2g ),triangular (as shown in FIG. 2d ), quadrilateral (as shown in FIG. 2d ),pentagonal (as shown in FIG. 2c ), annular (as shown in FIG. 2c ), oranother regular or irregular shape. Shape sizes of the plurality ofsupport force nozzles 111 or the plurality of openings 112 may be thesame (as shown in FIG. 2c to FIG. 2e as well as FIG. 2g ), or may bedifferent (as shown in FIG. 2f ). Shapes of the plurality of supportforce nozzles 111 or the plurality of openings 112 may be the same ormay be different. A shape of the plurality of support force nozzles 111and a shape of the plurality of openings 112 may be the same (as shownin FIG. 2b as well as FIG. 2e to FIG. 2g ), or may be different (asshown in FIG. 2c and FIG. 2d ). Intervals between any one of every twoadjacent support force nozzles 111, every two adjacent openings 112, andevery two adjacent support force nozzle and opening may be the same, ormay be different.

The plurality of openings 112 may make a first gas flowed back to thenozzle portion flow out of the air-bearing chuck, and the plurality ofopenings 112 may also be connected to an apparatus for providing suctionforce, to make the plurality of openings transmit a second gas toprovide suction force, which is not specifically limited in the presentapplication.

According to the technical solutions provided in the embodiments of thepresent application, a plurality of support force nozzles and aplurality of openings that are alternately arranged are disposed on anair-bearing chuck, so that the plurality of support force nozzles andthe plurality of openings are uniformly distributed, which helps absorb,by utilizing the plurality of openings, a first gas that flows back to anozzle portion, and avoid an impact of the first gas that has flowedback to the nozzle portion on stability of a supported object floatingabove the air-bearing chuck, thereby keeping the supported object suchas a wafer stably floating up on one side, away from a top surface ofthe nozzle portion, of an air cushion. Since there is no need to use aclamping tool to clamp the wafer during measurement, a shape of thewafer is not affected, thus reducing errors during measurement of thewafer.

In an embodiment of the present application, the plurality of openings112 include a plurality of suction force nozzles 1121. The gas channelportion 120 further includes a second gas channel 122, and the secondgas channel 122 is configured to transmit a second gas to the pluralityof suction force nozzles 1121 to provide suction force. It should beunderstood that, the air cushion 10 may be generated by a gas ejectedfrom the plurality of support force nozzles 111 and a gas sucked fromthe plurality of suction force nozzles. The air cushion 10 is configuredto keep a supported object such as a wafer floating up on one side, awayfrom the top surface of the nozzle portion 110, of the air cushion. Thefirst gas channel 121 may be provided with a pipeline connected to theplurality of support force nozzles 111, to transmit the first gas to theplurality of support force nozzles 111, thereby providing support force.Alternatively, the nozzle portion may be provided with a plurality ofthrough holes that are corresponding to the plurality of support forcenozzles 111 and communicated with a plurality of through holes disposedon the first gas channel, thereby transmitting the first gas to theplurality of support force nozzles 111 to provide support force, whichis not specifically limited in the embodiment of the presentapplication. The first gas channel 121 and the second gas channel 122may be set to have two layers of independent structures in the gaschannel portion 120, or may be set to have an overall structure in whichthe first gas channel 121 and the second gas channel 122 are staggeredwith each other but does not affect each other, as long as the first gaschannel 121 may transmit the first gas to the plurality of support forcenozzles 111 to provide support force, and the second gas channel 122 maytransmit the second gas to the plurality of suction force nozzles 1121to provide suction force, which is not specifically limited in theembodiment of the present application. The second gas channel 122 andthe first gas channel 121 may be disposed in a same manner or differentmanners, and there may be one or more first gas channels 121 or secondgas channels 122, which is not specifically limited in the embodiment ofthe present application. A flow rate of a gas in both the first gaschannel 121 and the second gas channel 122 may be controlled by using adevice such as a controller or an air pressure regulator, or may becontrolled by using a plurality of combined devices such as a controllerand an air pressure regulator, or may be controlled by using computersoftware. A control method of the flow rate of the gas in both the firstgas channel 121 and the second gas channel 122 is not specificallylimited in the embodiment of the present application.

In the embodiment of the present application, a plurality of supportforce nozzles and a plurality of suction force nozzles that arealternately arranged are disposed on an air-bearing chuck, and an aircushion is generated above a top surface of a nozzle portion, whichhelps keep a supported object such as a wafer supported by the aircushion stably floating up on one side, away from the top surface of thenozzle portion, of the air cushion. Since there is no need to use aclamping tool to clamp the wafer during measurement, a shape of thewafer is not affected, thus reducing errors during measurement of thewafer.

In an embodiment of the present application, the plurality of openings112 include a plurality of flow guide holes, the plurality of flow guideholes are configured to guide the first gas ejected from the pluralityof support force nozzles to flow back to the nozzle portion when thefirst gas encounters a to-be-measured object, the gas channel portion120 further includes a third gas channel 123, and the third gas channel123 is configured to make the first gas that has flowed back to thenozzle portion flow out of the air-bearing chuck.

The plurality of flow guide holes 112 are configured to guide the firstgas ejected from the plurality of support force nozzles 111 to flow backto the nozzle portion 110 when the first gas encounters a to-be-measuredobject such as the wafer. One or more corresponding support forcenozzles may be disposed for one flow guide hole, or one or morecorresponding flow guide holes may be disposed for one support forcenozzle, as long as it may be ensured that a flow guide hole is provided,when the first gas ejected from each support force nozzle flows back tothe nozzle portion, to make the first gas that has flowed back to thenozzle portion flow out of the air-bearing chuck, which is notspecifically limited in the present application.

In some specific implementation modes, the plurality of openings 112 mayall be flow guide holes, or may all be suction force nozzles. Adisposing manner of the third gas channel 123 may be the same as that ofthe second gas channel 122. The second gas channel 122 may be replacedwith the third gas channel 123, and the third gas channel 123 isconfigured to make the first gas that has flowed back to the nozzleportion flow out of the air-bearing chuck.

In some other specific implementation modes, when suction force arerequired to provide, the plurality of openings 112 may all be configuredas suction force nozzles; and when no suction force are required toprovide, the plurality of openings may all be configured as flow guideholes. The second gas channel 122 may be configured to not only transmitthe second gas to the plurality of suction force nozzles to providesuction force, but also make the first gas that has flowed back to thenozzle portion flow out of the air-bearing chuck.

In some other specific implementation modes, some of the plurality ofopenings 112 may be flow guide holes, the other openings 112 may besuction force nozzles, and the plurality of flow guide holes may bedisposed alternately with the plurality of suction force nozzles. Thesecond gas channel 122 may be only configured to transmit the second gasto the plurality of suction force nozzles to provide suction force, andthe third gas channel 123 may be only configured to make the first gasthat has flowed back to the nozzle portion flow out of the air-bearingchuck.

In the embodiments of the present application, flow guide holes and athird gas channel are disposed, which makes a first gas that has flowedback to a nozzle portion flow out of an air-bearing chuck, and helpsensure that a wafer is not affected by the first gas that has flowedback and is kept stably floating up on a top surface of the nozzleportion. In addition, the third gas channel is disposed, so that thefirst gas that has flowed back to the nozzle portion is made flow out ofthe air-bearing chuck, to generate a stable air cushion.

In an embodiment of the present application, the plurality of supportforce nozzles 111 and the plurality of openings 112 are arranged in anaxisymmetric pattern on the top surface 1 of the nozzle portion 110.

It should be understood that, the axisymmetric pattern arranged by theplurality of support force nozzles 111 and the plurality of openings 112may have only one axis of symmetry (as shown in FIG. 2d ), or may have aplurality of axes of symmetry (as shown in FIG. 2c as well as FIG. 2e toFIG. 2g ).

In the embodiment of the present application, a plurality of supportforce nozzles and a plurality of openings are arranged in anaxisymmetric pattern on a top surface of a nozzle portion, so that bothnumbers and shapes of support force nozzles and openings disposed onboth sides of an axis of symmetry are the same, which helps keep asupported object such as a wafer supported by an air cushion floating upon a plane at a same height as the top surface of the nozzle portion.

In an embodiment of the present application, adjacent nozzles in theplurality of support force nozzles 111 and the plurality of openings 112are arranged at an equal interval or unequal interval.

It should be understood that, adjacent nozzles in the plurality ofsupport force nozzles 111 and the plurality of openings 112 may bearranged at an equal interval or unequal interval, as long as the wafermay be kept stably floating up on the air-bearing chuck. When theplurality of support force nozzles 111 and the plurality of openings 112are arranged in concentric nozzle rings, adjacent nozzles on a samenozzle ring may be arranged at an equal interval, or adjacent nozzles ontwo adjacent concentric nozzle rings are arranged at an equal interval,or adjacent nozzles on a same nozzle ring may be arranged at an intervalequal to an interval between adjacent nozzles arranged on two adjacentconcentric nozzle rings. When the plurality of support force nozzles 111and the plurality of openings 112 are arranged on a plurality ofparallel lines, adjacent nozzles on a same parallel line may be arrangedat an equal interval, or adjacent nozzles on two adjacent parallel linesare arranged at an equal interval, or adjacent nozzles on a sameparallel line may be arranged at an interval equal to an intervalbetween adjacent nozzles arranged on two adjacent parallel lines.

In the embodiment of the present application, when adjacent nozzles in aplurality of support force nozzles and a plurality of openings aredisposed at an equal interval or unequal interval, a correspondingopening is disposed around each support force nozzle, so that a wafermay be kept stably floating up on one side, away from a top surface of anozzle portion, of an air cushion. If the plurality of openings includea plurality of suction force nozzles, when adjacent nozzles in theplurality of support force nozzles and the plurality of suction forcenozzles are set to be arranged at an equal interval, support force andsuction force may be further equalized, which further helps keep asupported object such as a wafer supported by the air cushion stablyfloating up on one side, away from the top surface of the nozzleportion, of the air cushion. If the plurality of openings include aplurality of flow guide holes, when adjacent nozzles in the plurality ofsupport force nozzles and the plurality of flow guide holes are set tobe arranged at an equal interval, each time the first gas flows back tothe air-bearing chuck, the first gas may flow out of the air-bearingchuck through the plurality of flow guide holes.

In some specific implementation modes, the plurality of support forcenozzles 111 and the plurality of openings 112 are arranged in aCartesian coordinate system or a polar coordinate system.

A plurality of support force nozzles and a plurality of openings arearranged in a Cartesian coordinate system or a polar coordinate system,so that the plurality of support force nozzles and the plurality ofopenings are arranged on a top surface of a nozzle portion moreuniformly, which further helps generate an air cushion above a topsurface of a nozzle portion.

In some specific implementation modes, shapes of the plurality ofsupport force nozzles and the plurality of openings include one or moreof a triangle, an oval, an annular ring, and a circle.

It should be understood that, the shapes of the plurality of supportforce nozzles and the plurality of openings include but are not limitedto one or more of a triangle, an oval, an annular ring, a circle, andanother regular or irregular shape, which is not specifically limited inthe present application.

The shapes of the plurality of support force nozzles and the pluralityof openings are set to include one or more of a triangle, an oval, anannular ring, a circle, and another regular or irregular shape, so thata stable air cushion is generated above a top surface of a nozzleportion by utilizing a plurality of manners.

FIG. 3a is a schematic top view of the first gas channel 121 in FIG. 2b. FIG. 3b is a schematic top view of the second gas channel 122 in FIG.2 b. FIG. 4a is a schematic top view of the first gas channel 121 inFIG. 2 e. FIG. 4b is a schematic top view of the second gas channel 122in FIG. 2 e.

In some specific implementation modes, referring to FIG. 3 a, the firstgas channel 121 includes a first annular channel 1211 and a plurality offirst channels 1212 connected to the first annular channel 1211.Referring to FIG. 3 b, the second gas channel 122 includes a secondannular channel 1221 and a plurality of second channels 1222 connectedto the second annular channel 1221.

In some other specific implementation modes, referring to FIG. 4 a, thefirst gas channel 121 includes a first annular channel 1211′ and aplurality of first channels 1212′ connected to the first annular channel1211′. Referring to FIG. 4 b, the second gas channel 122 includes asecond annular channel 1221′ and a plurality of second channels 1222′connected to the second annular channel 1221′.

It should be understood that, the first annular channel or the secondannular channel may be an annular channel farthest from the center of anair-bearing chuck (as shown in FIG. 3 a, FIG. 3b and FIG. 4b ), may bean annular channel closest to the center of the air-bearing chuck (asshown in FIG. 4a ), or may be an annular channel located at any positionon the air-bearing chuck, which is not specifically limited in theembodiment of the present application.

According to technical solutions provided in the embodiments of thepresent application, a structure of a first gas channel is set toinclude a first annular channel and a plurality of first channelsconnected to the first annular channel, and a structure of a second gaschannel is set to include a second annular channel and a plurality ofsecond channels connected to the second annular channel. Thus, thestructures of the first gas channel and the second gas channel are setas a whole, making a flow rate in the first gas channel or the secondgas channel be uniform and also be regulated uniformly.

FIG. 5 is a schematic structural diagram of an air-bearing chuck 300according to another embodiment of the present application. Theair-bearing chuck further includes an air pressure regulator 130. Theair pressure regulator 130 is configured to regulate a flow rate of agas in each of a first gas channel 121 and a second gas channel 122 tohold a wafer at a predetermined distance from a top surface of a nozzleportion, so as to measure a geometry of the wafer, and the geometry ofthe wafer includes one or more of a thickness and a shape of the wafer.

It should be understood that, the air pressure regulator 130 may be ageneral term of two regulators respectively configured to regulate aflow rate of a gas in the first gas channel 121 and a flow rate of a gasin the second gas channel 122, or may be a regulator configured tosimultaneously regulate the flow rate of the gas in both the first gaschannel 121 and the second gas channel 122. The air pressure regulator130 may be disposed on a side of a gas channel portion 120, or may bedisposed below the gas channel portion 120.

According to the technical solution provided in the embodiment of thepresent application, an air pressure regulator is disposed, so that aflow rate of a gas in a first gas channel and a flow rate of a gas in asecond gas channel may be effectively regulated, further helping controla height and stability of an air cushion generated above a top surfaceof a nozzle portion.

In an embodiment of the present application, the air-bearing chuck 300further includes a controller 140. The controller 140 is configured tocontrol the air pressure regulator 130 to regulate the flow rate of thegas in each of the first gas channel 121 and the second gas channel 122to hold the wafer at a predetermined distance D from the top surface ofthe nozzle portion, so as to measure the geometry of the wafer.

It should be understood that, the predetermined distance D may beunderstood as a height of an air cushion 10 or a floating height. Aspecific value of the predetermined distance may be adjusted accordingto actual requirements.

According to the embodiment of the present application, an air pressureregulator is controlled by a controller to regulate a flow rate of a gasin each of a first gas channel and a second gas channel, so thataccuracy of regulating the flow rate of the gas in each of the first gaschannel and the second gas channel can be effectively improved, and whenan air-bearing chuck is configured to hold a wafer at a predetermineddistance from a top surface of a nozzle portion, the predetermineddistance can be accurately adjusted.

In an embodiment of the present application, the predetermined distanceD ranges from 0 μm to 50 μm when the air-bearing chuck is configured tomeasure the flatness of the wafer.

It should be understood that, the predetermined distance D may be, forexample, 0 μm, 5 μm, 10 μm, 20 μm, 30 μm, or 50 μm.

According to the embodiment of the present application, thepredetermined distance D is set to range from 0 μm to 50 μm, which helpsmaintain a flatness of a back surface of a wafer to be almost as flat asa surface of an air-bearing chuck under an action of suction force whenthe air-bearing chuck is configured to support the wafer, and furtherhelps apply the air-bearing chuck to wafer flatness measurement after ashape of the surface of the air-bearing chuck is calibrated.

In an embodiment of the present application, the predetermined distanceD ranges from 60 μm to 1500 μm when the air-bearing chuck is configuredto measure the shape of the wafer.

It should be understood that, the predetermined distance D may be, forexample, 60 μm, 300 μm, 350 μm, 1000 μm, or 1500 μm, which is notspecifically limited in the embodiment of the present application.

According to the embodiment of the present application, a predetermineddistance D is set to range from 60 μm to 1500 μm, so that any change ofa wafer shape due to external force is avoided when an air-bearing chuckis configured to support the wafer, and thus an original state of thewafer can be effectively maintained, helping ensure measurement accuracywhen the air-bearing chuck is applied to shape measurement.

FIG. 6 is a schematic structural diagram of an air-bearing chuck 400according to still another embodiment of the present application. Adisposing manner of a second gas channel is similar to that of a thirdgas channel. Herein the second gas channel is taken as an example fordescription. As shown in FIG. 6, this embodiment has the followingdifferences from the embodiment illustrated in FIG. 2 a: A plurality offirst gas through holes 113 corresponding to a plurality of supportforce nozzles 111 and a plurality of second gas through holes 114corresponding to a plurality of suction force nozzles 1121 are disposedon both a nozzle portion 110 and a gas channel portion 120. A first gaschannel 121 is connected to the plurality of support force nozzles 111through the plurality of first gas through holes 113, and a second gaschannel 122 is connected to the plurality of suction force nozzles 1121through the plurality of second gas through holes 114.

It should be understood that the plurality of first gas through holes113 may be directly integrated with the first gas channel 121, or may beconnected to the first gas channel 121 by screws or adhesives, or may beconnected by a pipe embedded in the first gas channel 121, which is notspecifically limited in the embodiment of the present application. Thefirst gas channel 121 and the second gas channel 122 may be located ondifferent planes, or may be located on a same plane, which is notspecifically limited in the embodiment of the present application.

According to the technical solution provided in the embodiment of thepresent application, a plurality of first gas through holescorresponding to a plurality of support force nozzles and a plurality ofsecond gas through holes corresponding to the plurality of suction forcenozzles are disposed on a nozzle portion and a gas channel portion. Afirst gas channel is connected to the plurality of support force nozzlesthrough the plurality of first gas through holes, and a second gaschannel is connected to the plurality of suction force nozzles throughthe plurality of second gas through holes, so that a gas in the firstgas channel is transmitted to a position above a top surface of thenozzle portion through the plurality of first gas through holes and theplurality of support force nozzles, a gas in the second gas channel issucked out of an air-bearing chuck through the plurality of second gasthrough holes and a plurality of suction force nozzles, and a stable aircushion is generated under a combined action of the two manners.

In an embodiment of the present application, the gas channel portion 120includes a first gas layer 123 and a second gas layer 124 that arestacked. The first gas channel 121 is located in the first gas layer123, and the second gas channel 122 is located in the second gas layer124.

It should be understood that, the first gas layer 123 may be locatedabove the second gas layer 124, or may be located below the second gaslayer 124, which is not specifically limited in the embodiment of thepresent application.

According to the embodiment of the present application, a first gaschannel and a second gas channel are respectively disposed in a firstgas layer and a second gas layer that are stacked in a gas channelportion, so that the first gas channel and the second gas channel arelocated in different planes, which helps the first gas channel and thesecond gas channel independently transmit a first gas and a second gas.

FIG. 7 is a schematic structural diagram of an air-bearing chuckaccording to yet another embodiment of the present application. Theembodiment illustrated in FIG. 7 is a modified example of the embodimentillustrated in FIG. 6. A difference between the two embodiments lies inthat, in an air-bearing chuck 500 of the embodiment illustrated in FIG.6, the first gas layer 123 is provided with a first groove 1231 foraccommodating the first gas channel 121, and the second gas layer 124 isprovided with a second groove 1241 for accommodating the second gaschannel 122. A plurality of support force pipes 1131 connected with thefirst gas channel 121 are disposed in the plurality of first gas throughholes 113, and a plurality of suction force pipes 1141 connected withthe second gas channel 122 are disposed in the plurality of secondthrough holes 114.

It should be understood that, a manner in which the first groove 1231 isconfigured for accommodating the first gas channel 121 may be that thefirst groove 1231 is equivalent to the first gas channel 121, may bethat the first gas channel 121 is embedded in the first groove 1231, ormay be another manner, which is not specifically limited in theembodiment of the present application. A manner in which the secondgroove 1241 is configured for accommodating the second gas channel 122may be the same as or different from the manner in which the firstgroove 1231 is configured for accommodating the first gas channel 121,which is not specifically limited in the embodiment of the presentapplication.

According to the technical solution provided in the embodiment of thepresent application, a first gas layer is provided with a first groovefor accommodating a first gas channel, and a second gas layer isprovided with a second groove for accommodating a second gas channel, sothat a space is provided for each of the first gas channel and thesecond gas channel on the first gas layer and the second gas layer,respectively, so as to ensure that a first gas is transmitted to aplurality of support force nozzles through the first gas channel toprovide support force and a second gas is transmitted to a plurality ofsuction force nozzles through the second gas channel to provide suctionforce.

FIG. 8a shows an air-bearing chuck with vacuum nozzles and pressurenozzles for holding a wafer on an air cushion. The embodimentillustrated in FIG. 8a is an example of the embodiment illustrated inFIG. 2a to FIG. 2 f. A difference between the two embodiments lies inthat, in an air-bearing chuck 600A of the embodiment illustrated in FIG.8 a, pressure nozzles 601 are an exemplary implementation mode of thesupport force nozzles 111 in the embodiment illustrated in FIG. 2a toFIG. 2 f, vacuum nozzles 602 are an exemplary implementation mode of theopenings 112 in the embodiment illustrated in FIG. 2a to FIG. 2 f, andthe plurality of pressure nozzles 601 and the plurality of vacuumnozzles 602 are arranged alternately in concentric nozzle rings equallyspaced at an interval of ΔR. In some specific implementation modes, asshown in FIG. 8a , the concentric nozzle rings are concentric rings. Ona same nozzle ring of the concentric nozzle rings, the plurality ofpressure nozzles 601 and the plurality of vacuum nozzles 602 arearranged with a single pressure nozzle 601 and a single vacuum nozzle602 as repeating units. The plurality of pressure nozzles 601 and theplurality of vacuum nozzles 602 are in a circular shape, and both shapesand sizes of the plurality of pressure nozzles 601 and the plurality ofvacuum nozzles 602 are the same, which is not specifically limited inthe embodiment of the present application.

It should be understood that, ΔR denotes an interval between every twoadjacent nozzle rings of the plurality of concentric nozzle rings.

According to the technical solution provided in the embodiment of thepresent application, a plurality of pressure nozzles and a plurality ofvacuum nozzles are arranged in concentric nozzle rings, and distancesbetween every two adjacent concentric nozzle rings of the plurality ofconcentric nozzle rings are the same, so that the plurality of pressurenozzles and the plurality of vacuum nozzles are uniformly arranged on atop surface of a nozzle portion, which facilitates equilibriumdistribution of vacuum suction force and pressure support force on anyone of the concentric nozzle rings, thereby generating a stable aircushion on the top surface of the nozzle portion.

Vacuum suction force and pressure support force may keep a waferfloating up on an air cushion of a few microns to hundreds of micronsabove the air-bearing chuck 600A. The thinner the air cushion, thegreater the air flow, and the stiffer the air bearing. With a properflow rate of vacuum and pressure, the air bearing may be very stiff(e.g., larger than 1 N/um). For an air gap of about 20 μm, the airbearing also has a significant capability to keep the wafer flat.However, the stiffness of a 100 μm thick air bearing may be as low asone-tenth of 1 N/μm, where force that deforms a shape of the wafer isvery small.

To measure a wafer flatness or TTV from a front surface of the wafer, aback surface of the wafer may be flattened by the air-bearing chuck 600Aand matched with a surface of the air-bearing chuck 600A. The frontsurface of the wafer is a surface, away from the air-bearing chuck, ofthe wafer, and is not limited to a specific surface of the wafer. Whenthe air gap is set at a proper height (e.g., 15 μm to 20 μm), artifactsare not detected on the air-bearing chuck 600A. To measure a shape ofthe wafer, the wafer is floated up on the surface of the air-bearingchuck 600A, with the air gap ranging from 60 μm to 300 μm, and the waferis supported by the air cushion generated by the air-bearing chuck 600Aand maintains its original shape due to the suction force being verysmall at large air gap.

For example, in a Wafer Geometry Tool (WGT) for wafer flatness and shapemeasurement, the air-bearing chuck 600A may have the following features,as shown in FIG. 8 a.

(1) The pressure nozzles 601 and vacuum nozzles 602 are arrangedalternately in concentric and axisymmetric nozzle rings.

(2) A radius of the nozzle ring farthest from the center of the nozzlerings is smaller than the radius of the wafer. The nozzles, such as thevacuum nozzles or the pressure nozzles, extend from the center of thenozzle rings all the way out to a position about 0 mm to 20 mm (greaterthan 0), such as 2 mm to 4 mm, away from the circumference of theair-bearing chuck 600A, so as to support the wafer. For example, for a200 mm chuck, the nozzles, such as the pressure nozzles 601 or vacuumnozzles 602, extend radially such that the centers of the last set ofnozzles are located on a circumference of a circle with a diameter ofany one of 199 mm, 198 mm, 196 mm, 190 mm, and 180 mm on the air-bearingchuck. The surface of the air-bearing chuck 600A may be larger than thatof the wafer, so that the wafer does not overhang beyond the edge of theair-bearing chuck 600A.

In an embodiment of the present application, a radius of the nozzle ringfarthest from the center of the plurality of concentric nozzle rings is0 mm to 20 mm smaller than the radius of the air-bearing chuck.

In the embodiment of the present application, a radius of a nozzle ring,farthest from the center of an air-bearing chuck, of a plurality ofconcentric nozzle rings is set to be 0 mm-20 mm smaller than a radius ofthe air-bearing chuck, which helps keep, when a wafer is supported byutilizing the air-bearing chuck, the wafer floating above a top surfaceof the air-bearing chuck in an evenly stressed manner, and furtherfacilitates controlling a distance at which the wafer is held from thetop surface of the air-bearing chuck by regulating magnitude of vacuumsuction force and pressure support force.

(3) In an embodiment of the present application, each vacuum nozzle andan adjacent pressure nozzle that are on any one of the plurality ofconcentric nozzle rings are tangentially spaced at a constant distanceΔT.

It should be understood that, ΔR and ΔT may be the same or different,which is not specifically limited in the embodiment of the presentapplication.

In the embodiment of the present application, each vacuum nozzle and anadjacent pressure nozzle that are on any nozzle ring are set to betangentially spaced at a constant distance ΔT, so that vacuum nozzlesand pressure nozzles on a same nozzle ring are uniformly distributed,which helps equalize vacuum suction force and pressure support force,and further makes an air cushion have a uniform height above the samenozzle ring.

In an embodiment of the present application, to keep nozzlestangentially spaced at a constant distance, as a distance between eachnozzle ring of the plurality of concentric nozzle rings and the centerof the air-bearing chuck increases, a total number of nozzles on thenozzle ring is set to increase in an even number m, for example,expressed by a formula: N=m×n, and m denotes an increased number ofnozzles (m=2, 4, 6, 8, 10, or . . . ), n is the n^(th) nozzle ring of aspecific concentric nozzle ring, and N denotes a number of nozzles pernozzle ring.

It should be understood that, the even number includes but is notlimited to 2, 4, 6, 8, or 10.

In the embodiment of the present application, as a distance between eachnozzle ring of a plurality of concentric nozzle rings and the center ofan air-bearing chuck increases, a total number of nozzles on the nozzlering is set to increase in an even number, so that an increased numberof support force nozzles and an increased number of suction forcenozzles are the same on each concentric nozzle ring, which further helpsequalize vacuum suction force and pressure support force.

In an embodiment of the present application, a difference between ΔR andΔT is less than 5 mm.

Specifically, as the radius increases, there is an increase of 6 nozzlesper nozzle ring while the tangential separation between nozzles ismaintained at a constant. To achieve this, the following formula isused: N=6×n, and n=0 is the first “nozzle ring” at the center of thewafer 400, and m=6. The number “6” is selected in order to achieve aboutthe same displacement between nozzles in both the radial and tangentialdirections as well when m=6.

The selection of the number of “6” is based on the following method. Theseparation ΔT between the pressure nozzles 601 and the vacuum nozzles602 in tangential direction may be the same across the whole air-bearingchuck 600A. The adjacent nozzle rings are separated by a constantdistance ΔR. For a given ΔR, ΔT may be calculated based on the followingmethod.

It is assumed that, as radius increases, a quantity of nozzles for eachadjacent nozzle ring increases by an even integer m, and even integer isused because vacuum nozzle and pressure nozzle are paired.

N = m × n

Where “N” denotes the number of nozzles per nozzle ring.

“n” denotes the n^(th) nozzle ring of a specific nozzle ring; and everytwo adjacent nozzle rings are separated by ΔR, and the radius of then^(th) nozzle ring is Rn=n×ΔR.

“m” is an even-integer (such as 2, 4, 6, 8, 10) because the number ofnozzles increases in pairs.

ΔT = 2p × n × ΔR/N = 2p × ΔR/m = (2p/6) × ΔR

Where p is equal to π. When m=6, ΔR and ΔT have almost the same valuebased on the above formula.

It should be understood that, values of ΔR and ΔT may be completely thesame, or may be approximately the same. Specific values of ΔR and ΔT arenot limited as long as a difference between ΔR and ΔT is less than 5 mm.For example, as shown in FIG. 8 a, ΔR=7.9 mm, and ΔT=6.2 mm. Since thedifference between ΔR and ΔT is 1.7 mm, it may be considered that ΔR andΔT are approximately the same.

In the embodiment of the present application, a difference between ΔRand ΔT is set to be less than 5 mm, for example, a difference betweennumbers of nozzles on every two adjacent concentric nozzle rings of aplurality of concentric nozzle rings is set to be 6, so that values ofΔR and ΔT are approximately the same, which helps the air-bearing chuckprovide vacuum suction force and pressure support force that areuniformly distributed, and further facilitates generation of a stableair cushion with a uniform height.

(4) A chuck flatness of a WGT 200 (a wafer geometry tool for measuringthe wafer geometry of 200 mm wafers) may be less than or equal to 1.5μm. A chuck flatness of a WGT 300 (a wafer geometry tool for measuringthe wafer geometry of 300 mm wafers) may be less than or equal to 2 μm.For example, when applied to flatness measurement of an advanced wafer,a chuck flatness of a WGT 300 may be 0.5 μm or even less than 0.5 μm.

(5) The chuck surface polished to be mirror like finish, higher than orequal to level N4 per ISO standard.

In an embodiment of the present application, the air-bearing chuck 600Ahas a mirror polished surface higher than or equal to level N4 inaccordance with an ISO standard.

In the embodiment of the present application, an air-bearing chuck isset to have a mirror surface higher than or equal to level N4 inaccordance with an ISO standard, so that surface defects of theair-bearing chuck are reduced, and a surface of the air-bearing chuck iskept sufficiently flat.

(6) A diameter of the air-bearing chuck 600A may be 10 mm greater than adiameter of the wafer. An area of the air-bearing chuck that is largerthan the wafer may be configured for calibration during wafermeasurement since this part is not blocked by the wafer.

(7) There are three wafer grippers 603, two fixed (90 degrees apart,configured to fix any two wafer grippers 603), and one actuating griperfor center wafer. Force on the wafer may be adjustable (e.g., 0.05 lb-1lb).

(8) There are four lift pins 604 that may lift the wafer up from thechuck 600A in a smooth manner, to facilitate removal of the wafer fromthe chuck.

FIG. 8b shows an exemplary air-bearing chuck with vacuum nozzles andpressure nozzles. In air-bearing chuck 600B, the vacuum nozzles andpressure nozzles are arranged according to ΔR and ΔT shown in FIG. 8 b,ΔR=11.0 mm, and ΔT=9.0 mm. Since the difference between ΔR and ΔT is 2mm, it may be considered that ΔR and ΔT are approximately the same.

FIG. 8c is a schematic diagram of connection layers of pressure nozzlesand vacuum nozzles of an air-bearing chuck. FIG. 8c provides a top viewof stacked layers of the air-bearing chuck 600C. The stacked layersinclude a pressure manifold layer 610 c, a vacuum manifold layer 620 c,and a top chuck layer 630 c. The vacuum manifold layer 620 c connectsall the vacuum channels 621 c and vacuum supply. The pressure manifoldlayer 610 c connects all the pressure channels 611 c and pressuresupply. The top chuck layer 630 c includes a plurality of through holesconnecting the vacuum channels 621 c in the vacuum manifold layer 620 cto the vacuum nozzles on the top surface of the top chuck layer 630 c.The top chuck layer 630 c further includes additional through holesconnecting the pressure channels 611 c in the pressure manifold layer610 c to the pressure nozzles on the top surface of the top chuck layer630 c. The through holes for vacuum and pressure are arranged in analternating fashion corresponding to the vacuum and pressure nozzlearrangements shown in FIG. 8a and FIG. 8 b.

FIG. 8d is a schematic side view of a stacked structure of anair-bearing chuck 600D according to an embodiment of the presentapplication. The embodiment illustrated in FIG. 8d is an example of theembodiment illustrated in FIG. 2 a. A difference between the twoembodiments lies in that, in the embodiment illustrated in FIG. 8 d, atop chuck layer 630 d is corresponding to the nozzle portion 110 in theembodiment illustrated in FIG. 2 a, a combined structure of a vacuummanifold layer 620 d and a pressure manifold layer 610 d iscorresponding to the gas channel portion 120 in the embodimentillustrated in FIG. 2a . The air-bearing chuck 600D includes a top chucklayer 630 d, a vacuum manifold layer 620 d, and a pressure manifoldlayer 610 d. There are alternating through holes 631 d and 632 dconnecting the vacuum channels 621 d and pressure channels 611 d,respectively, to the vacuum nozzles and pressure nozzles on the topsurface of the air-bearing chuck 600D. As shown in the side view of theair-bearing chuck of FIG. 8 d, the separation ΔT between the alternatingvacuum nozzles and pressure nozzles may be substantially the same.

FIG. 8e is a schematic side view of a stacked structure of anair-bearing chuck 600E according to another embodiment of the presentapplication. The embodiment illustrated in FIG. 8e is an example of theembodiment illustrated in FIG. 2 a. A top plate 610 e is correspondingto the nozzle portion 110 in the embodiment illustrated in FIG. 2 a, anda manifold plate 620 e is corresponding to the gas channel portion 120in the embodiment illustrated in FIG. 2 a. In addition, the stackedstructure may include a top plate 610 e, a back cover plate 630 e, and amanifold plate 620 e sandwiched between the top plate 610 e and the backcover plate 630 e. The top plate 610 e may be composed of any one ofaluminum, ceramic, glass, and microcrystalline silicon, and a thicknessof the top plate 610 e ranges from 10 mm to 60 mm. Similar to theembodiment illustrated in FIG. 8 d, through holes 611 e and 612 ealternately disposed in the top plate 610 e provide pressure supportforce and vacuum suction force, respectively, to keep the wafer floatingon an air cushion.

It should be understood that, a diameter of the through holes 611 e and612 e may range from 1 to 3 mm, further, may range from 1.25 to 1.5 mm.The diameter of the through holes may be the same as or different from adiameter of nozzles disposed on a top surface of the top plate, which isnot specifically limited in the embodiment of the present application.

In an embodiment of the present application, a material of the nozzleportion, for example, the top plate 610 e, includes aluminum, glass,microcrystalline silicon, or ceramic. The material is rigid, and may bemirror polished. The top surface, obtained after being polished, of thenozzle portion is sufficiently flat, so that interference fringes areshown on the top surface of the nozzle portion.

It should be understood that, the material of the nozzle portion, forexample, the top plate 610 e, may be aluminum, glass, microcrystallinesilicon, or ceramic, and a thickness of the material ranges from 15 mmto 20 mm. In addition to aluminum, glass, microcrystalline silicon, orceramic, the material of the top plate 610 e may alternatively beanother rigid material that may be mirror-polished, which is notspecifically limited in the embodiment of the present application.

In the embodiment of the present application, a material of a nozzleportion is set to be aluminum, glass, microcrystalline silicon, orceramic, so that not only rigidity of the material is guaranteed, butalso a top surface of a top plate may be mirror polished; in addition,the selected material keeps a top surface, obtained after beingpolished, of the nozzle portion sufficiently flat, which helpsinterference fringes be shown on the top surface of the nozzle portion.

A top surface and a bottom surface of the manifold plate 620 e may eachhave one or more grooves in which a pressure channel 621 e and a vacuumchannel 622 e may be located, respectively. In an example illustrated inFIG. 8 e, the vacuum channel 622 e may be embedded in a groove on thetop surface of the manifold plate 620 e, and connects vacuum nozzles onthe top plate 610 e of the stacked structure to vacuum outlets 632 e ona bottom plate of the stacked structure through the through holes 612 e.Similarly, the pressure channel 621 e may be embedded in a groove on thebottom surface of the manifold plate 620 e, and connects pressurenozzles on the top plate 610 e of the stacked structure to pressureoutlets 631 e on the bottom plate of the stacked structure through thethrough holes 611 e. The grooves on the top surface and the bottomsurface of the manifold plate may be arranged according to the structureof the vacuum channel and the pressure channel, respectively, and may beseveral millimeters wide and several millimeters deep, for example, maybe 2 mm wide and 2 mm deep.

FIG. 8f shows a top surface of the top plate of the stacked structure inFIG. 8 e. The top surface 1 f of the top plate 610 e includes equally ornonequally spaced alternating pressure nozzles 601 f and vacuum nozzles602 f (or vacuum holes) with for example, 5 mm to 25 mm radial andtangential spacing, for another example, 8 mm to 12 mm radial andtangential spacing, respectively. The vacuum nozzles 602 f may have adiameter of several millimeters, such as 1.5 mm. The pressure nozzles601 f may have a diameter of several millimeters, such as 1.25 mm. Boththe vacuum nozzles 602 f and the pressure nozzles 601 f may havechamfers.

In some specific implementation modes, when a plurality of vacuumnozzles and a plurality of pressure nozzles are in a circular shape, adiameter of the plurality of vacuum nozzles and the plurality ofpressure nozzles ranges from 0.5 mm to 3 mm.

It should be understood that, the diameter of the plurality of vacuumnozzles and the plurality of pressure nozzles may be, such as, 0.5 mm,0.75 mm, 1 mm, 1.1 mm, 1.25 mm, 1.3 mm, 1.35 mm, 1.5 mm, 1.73 mm, 2 mm,or 3 mm. For example, the diameter of the plurality of vacuum nozzlesand the plurality of pressure nozzles ranges from 1.25 mm to 1.5 mm. Thediameter of the plurality of vacuum nozzles and the plurality ofpressure nozzles may be designed based on a size of an air-bearing chuckand density of nozzles required for generating an air cushion. Adiameter of the vacuum nozzles and a diameter of the pressure nozzlesmay be the same or different. The diameter and the diameter range of theplurality of vacuum nozzles and the plurality of pressure nozzles arenot specifically limited in the embodiment of the present application.

A diameter of a plurality of vacuum nozzles and a plurality of pressurenozzles is set to range from 0.5 mm to 3 mm, which helps arrange asufficient number of vacuum nozzles and pressure nozzles on a topsurface of a top plate, to generate a stable air cushion above the topsurface of the top plate.

FIG. 8g shows a bottom surface 1 g of the top plate 610 e of the stackedstructure in FIG. 8e , and shows the same pattern of pressure nozzles601 g and vacuum nozzles 602 g. The bottom surface 1 g may also includeM3.5 or M4 threaded holes 2 g for fastening the plates of the stackedstructure together and sealing the vacuum channels and pressurechannels. Alternatively, the glue may also be configured to hold theplates together, and this method may improve a flatness of the topsurface. If glue is configured, no M3.5 or M4 or any other threadedholes are required on the plate.

FIG. 8h is a top view of the manifold plate of the stacked structure inFIG. 8 e. All vacuum nozzles from the top plate are connected tocorresponding vacuum holes 612 h in the top surface 1 h of the manifoldplate 620 e. In comparison, all pressure nozzles from the top plate areconnected to corresponding pressure holes 611 h in the grooves on thetop surface the manifold plate 620 e, to form straight holes from thetop plate down through the manifold plate 620 e (as shown in FIG. 8e ),thereby connecting the pressure nozzles on the top plate to the pressurechannels 621 h (shown in FIG. 8i ) embedded in the grooves at the bottomof the manifold plate 620 e. In some specific implementation modes,vacuum channels 622 h on the top surface of the manifold plate 620 e maybe patterned as shown in FIG. 8h . The channels are aligned with thevacuum nozzles on the top plate and are connected by an outer circularchannel 623 h along the edge of the manifold plate 620 e. FIG. 8h alsoshows M3.5 or M4 threaded holes 2 g for fastening the plates of thestacked structure together. FIG. 8i is a bottom view of an exemplarymanifold plate 620 e of the stacked structure in FIG. 8 e. The pressurechannels or grooves 621 i may be in an inner ring-like pattern(“pressure supply ring”), and connects pressure holes that are throughthe manifold plate 620 e. Since a cross section of the pressure supplyring increases, the pressure supply ring may be less resistance. Thebottom view of FIG. 8i also shows the M3.5 or M4 threaded holes 2 gshown in the top view of FIG. 8 h. Although the bottom view also showsthe superimposed vacuum channels 622 h, it should be understood thatthis is only for illustrative purposes. As shown in FIG. 8 h, the actualvacuum channels 622 h are situated in grooves on the top surface of themanifold plate 620 e.

FIG. 8j is a top view of the back cover plate 630 e of the stackedstructure in FIG. 8 e. FIG. 8k is a bottom view of the back cover plate630 e of the stacked structure in FIG. 8e . As shown in FIG. 8 j, thetop surface 1 j of the back cover plate 630 e may be polished to sealthe manifold bottom surface of the manifold plate embedded with thepressure grooves. In some specific implementation modes, there are threeopenings 3 j for connecting the pressure channels from the bottomsurface of the manifold plate 620 e to a pressure fitting. In addition,there are three other openings 4 j for connecting the vacuum channelsfrom the top surface of the manifold plate to a vacuum fitting. The samepressure openings 3 k and vacuum openings 4 k are also shown in thebottom view of the back cover plate 630 e in FIG. 8 k. The top view ofthe back cover plate 630 e shown in FIG. 8j and the bottom view of theback cover plate 630 e shown in FIG. 8k also show M3.5 or M4 threadedholes 2 g for fastening the back cover plate to other plates in thestacked structure.

Although FIG. 8e to FIG. 8k show a stacked structure of an air-bearingchuck, and the stacked structure has pressure channels and vacuumchannels respectively located in grooves on the bottom surface and topsurface of the manifold layer, it should be understood that, thesechannels may alternatively be embedded in grooves of another layer. Forexample, the vacuum channels may be located in grooves on the bottomlayer of the top plate, and the pressure channels may be located ingrooves on the top layer of the back cover plate. Furthermore, it shouldbe understood that, the arrangement of the vacuum channels and thepressure channels may be interchangeable. In various specificimplementation modes, numbers of vacuum nozzles may be different,numbers of pressure nozzles may be different, or numbers of both ofvacuum nozzles and pressure nozzles may be different. Paths of thevacuum channels and pressure channels may be adjusted according to thenumber and position of the nozzles. Numbers of vacuum fittings andpressure fittings at the bottom of the stacked structure are notlimited, for example, may be three or more.

FIG. 9a and FIG. 9b are schematic structural diagrams of an exemplarymanifold chamber 900 according to an embodiment of the presentapplication. The manifold chamber 900 is an example of the gas channelportion 120 shown in FIG. 2 a. The manifold chamber 900 is configured toseparate pressure nozzles from vacuum nozzles. As shown in FIG. 9a andFIG. 9 b, the manifold chamber 900 includes a pressure manifold chamber921 and a vacuum manifold chamber 922. All vacuum nozzles are connectedto the vacuum manifold chamber 922. All pressure nozzles pass throughthe vacuum manifold chamber 922 and directly reach the pressure manifoldchamber 921 located below the vacuum manifold chamber 922. A computerfluid dynamics (Computational fluid dynamics, CFD) simulation shows thatsuch kind of manifold chamber greatly improves uniformity of the vacuumnozzles and the pressure nozzles. The manifold chamber may provide auniform amount of gas and optimize an increased channel size to thegreatest extent. In addition, a height of the chamber may be adjusted tominimize a change in orifice flow.

An air cushion configured to support a wafer also has a gas dampingcapability, which effectively isolates ground vibration and soundvibration, thus removing or reducing a need for sound isolation boxesand active vibration isolation systems.

There are other advantages of using the air-bearing chuck in the aboveembodiments. For example, accuracy of thickness measurement of a masklayer applied on a wafer may be improved. In a 3-D flash memory (3DNAND) process, thickness measurement of a highly non-transparent hardmask (or film) does not meet requirements because a conventional opticalmethod cannot be well applied to the non-transparent film.Characteristics of thickness measurement of a WGT wafer may beconfigured for thickness measurement of a hard mask. For example, twotypes of thickness measurement are performed: One is thicknessmeasurement on a pre-mask wafer (pre-mask, T_(Pre)), and the other isthickness measurement on a post-mask wafer (T_(post)).

T_(pre) = T₀ + E_RTE_pre T_(post) = T₁ + E_RTE_post

T₀and T₁ denote measured values of thicknesses of the pre-mask wafer andthe post-mask wafer, respectively. E_RTE_pre and E_RTE_post denote RayTracing Error (RTE) of the pre-mask wafer and the post-mask wafer,respectively.

Therefore, the thickness ΔT of the mask layer is as follows:ΔT=T_(post)−T_(pre)=(T₁−T₀)+(E_RTE_post−E_RTE_pre).

The wafer may be sharply warped after a mask is applied. As a result,RTE (namely, E_RTE_post−E_RTE_pre) may apparently affect measurementresults of T_(Pre) and T_(Post), causing significant errors during ΔTcalculation. After the mask layer is applied on a surface of the wafer,the wafer may be kept basically flat by utilizing suction forcegenerated by the air-bearing chuck, so that shapes of the pre-mask waferand the post-mask wafer are basically the same. Therefore, RTE isminimized (that is, E RTE-post−E_RTE_pre≈0), and accuracy of thicknessmeasurement is improved.

The air-bearing chuck may be configured to reduce or eliminate the raytracking errors of an interferometer by forcing a wafer with a largewarp to match a top surface of the air-bearing chuck, or may beconfigured to reduce warps of the post-mask wafer, so that a shape ofthe pre-mask wafer is consistent with a shape of the post-mask wafer.Therefore, ray tracing errors are eventually eliminated when a thicknessof a film is obtained by subtracting a thickness of a wafer obtainedbefore the film is deposited from a thickness of the wafer obtainedafter the film is deposited. When the method is applied to thicknessmeasurement of a non-transparent hard mask layer, ray tracing errorscaused by a large warp of the wafer can be greatly reduced.

In the present specification, “wafer geometry” may refer to wafer shapeparameters (e.g., bow and warp), as well as local flatness parameters(also referred to as local plainness parameters, such as Site Flatness(SFQR), Site flatness Back Ideal Range (SBIR), and Global Flatness BackIdeal Range (GBIR)). Wafer flatness, also referred to as Total ThicknessVariation (TTV), may refer to high density raw data (e.g., ≥4Mpixels/wafer) that may be configured for deriving SFQR, GBIR, and manyother related parameters. Flatness data is normally associated with bothfront surface and back surface information of a wafer. For example, thewafer shape parameters may be derived from a height map of a singlesurface, and the single surface may be a front surface or a back surfaceof a wafer, or may be medium of the two surfaces (e.g., wafer shapedefined by Semiconductor Equipment and Materials International (SEMI)).For advanced 300 mm wafer, there is a very small difference between ashape obtained by medium value of the front surface and the back surfaceof the wafer, a shape only obtained by the front surface of the wafer,and a shape only obtained by the back surface of the wafer. This isbecause the wafer shape is in the order of a few micron to a few hundredmicron, while TTV or GBIR is in the order of tens or hundreds ofnanometers. In a patterned wafer geometry tool, wafer shape may becalculated from either the front surface or the back surface, dependingon suppliers of the tools.

Wafer geometry tool (Wafer Geometry Tool, “WGT” for short) is ametrology tool that may be configured in Si wafer manufacturing fabs forcharacterizing wafer flatness, nano-topography and shape (e.g., bow andwarp), and may also be configured in glass wafer fabs. Typically, eachwafer has to be certified by WGT type of tools before shipping to acustomer. There are several existing tools serving this purpose. Forexample, capacitive sensor-based wafer geometry tools are widely used in200 mm wafer fabs. FIG. 10a is a schematic structural diagram of a dualFizeau interferometer-based tool. The tool may be configured to measurethe wafer geometry of 300 mm wafers. Interferometer-based wafer geometrytool has the advantage in both precision and throughput. Its precisionis about one to two magnitude better than that of capacitivesensor-based tool, despite of the fact that 300 mm wafer is more proneto vibration than that of 200 mm wafer. However, there have been nointerferometer-based 200 mm wafer geometry tool on the market.Capacitive sensor-based wafer geometry tools were designed for 250 nm,180 nm, and 130 nm, node processes. Capacitive sensor tool cannot keepup with the precision and throughput requirement for design nodessmaller than 90 nm.

FIG. 10b is a schematic structural diagram of a shearinginterferometer-based tool. The shearing interferometer may also beconfigured together with the air-bearing chuck in the presentapplication to measure geometries such as wafer shape and flatness.

WGT Architecture

The present application relates to a semiconductor device architecturefor measuring a wafer flatness and a wafer shape for various types ofwafers such as 200 mm wafers. The architecture may have better precisionand throughput than capacitive sensor or optical sensor-based scanningtools. Embodiments of the architecture in the present application mayalso be configured for 300 mm and 450 mm wafer geometry tools. Inaddition to wafer geometry tools, the architecture in the presentapplication may also be configured in patterned wafer geometry(Patterned Wafer Geometry, PWG) tools. An air cushion is configured inthe air-bearing chuck to support a wafer during measurement of the wafershape. The air-bearing film or air cushion of the air-bearing chuck hasvery small stiffness and exerts sufficient force on the wafer to help tokeep the shape unchanged, which is ideal for measuring of the wafershape.

FIG. 10c is a schematic structural diagram of an architecture formeasuring a wafer geometry. The architecture may perform the samemeasurement as a dual Fizeau tool, but at a fraction of the cost. Thearchitecture has many obvious advantages over existing dual Fizeau toolsin measuring a wafer shape. As shown in FIG. 10 c, an architecture 1000may include a single Fizeau interferometer. The single Fizeauinterferometer includes a camera 1002, a relay lens 1004, a PolarizationBeam Splitter or Combiner (PBSC) 1006, a light source (e.g., anillumination light) 1008, a collimator 1010, and a Transmission Flat(TF) 1012, all as shown in FIG. 10c . The operation of a Fizeauinterferometer is well known and thus is not described in detail herein.In this architecture, the single Fizeau interferometer is configured tomeasure the geometry of a wafer 1014. It should be understand that, thetransmission flat may also be referred to as a test flat, a transmissionflat, or the like. The architecture is not limited to the use of theFizeau interferometer, and another type of vertically incidentinterferometer may alternatively be configured, such as a grating-basedshearing interferometer.

As shown in FIG. 10 c, the wafer 1014 may be horizontally placed on anair cushion generated above a top surface of an air-bearing chuck 1016.The air-bearing chuck 1016 may include a plurality of alternatingpressure channels 1030 and vacuum channels (or guide channels) 1032, forgenerating and maintaining the air cushion above the top surface of theair-bearing chuck 1016. The air-bearing chuck 1016 may also include aZ-tip-and-tilt stage 1018, and the Z-tip-and-tilt stage 1018 may makethe air-bearing chuck 1016 be tipped and/or tilted. A plurality of liftpins 1020 may be configured to lift the wafer up from the top surface ofthe air-bearing chuck 1016.

In addition, referring to FIG. 10c , a combination of a capacitivesensor 1022 at the bottom of wafer 1014 (e.g., embedded in theair-bearing chuck 1016) and one or more optical position sensors 1026(bi-cell or PSD, Position Sensing Diode) along with a laser 1024 on thetop of the wafer 1014 are incorporated into the architecture 1000 tomeasure a thickness of the wafer 1014. FIG. 10d is a schematic diagramshowing positions of a position sensor and a capacitive sensor relativeto a wafer. The wafer may be a calibration wafer, or may be anotherto-be-measured object. FIG. 10e is a schematic diagram of calibration ofa position sensor. In combination with FIG. 10d and FIG. 10 e, aposition sensor reading Vx may be calibrated by utilizing a wafer 1011with a known thickness, namely, a calibration wafer 1011. A position ofthe position sensor may be correlated to a height of a top surface ofthe wafer. The capacitive sensor 1022 may be configured to measure aposition of a bottom surface of the wafer. The combined information ofthe top and bottom surface positions may be configured for accuratelydetermining the thickness of the wafer 1014. The elliptical structure inFIG. 10d and FIG. 10e represents a spot on a surface of the calibrationwafer 1011.

There is an added advantage of the bi-cell or PSD position sensordisposed at the top of wafer 1014. The position sensor reading may becorrelated directly to wafer thickness. The position sensor readingsabove the wafer 1014 may also tell the relative motion or vibrationbetween the wafer 1014 and the TF 1012. The vibration of the wafer maybe caused by one or more of the air-bearing chuck, flange and supportingmechanism, which cannot be sensed by the capacitive sensor 1022, becausethe capacitive sensor 1022 moves with the unit that includes the wafer1014 and the air-bearing chuck 1016.

The interferometer tool may be configured to calibrate the capacitivesensor and optical (bi-cell or PSD) position sensors. Both thecapacitive sensor 1022 and the optical (bi-cell or PSD) position sensors1026 may sense air-bearing stability, but only the optical (bi-cell orPSD) sensors may sense the vibration of chuck assembly. This may beuseful when there is a need to isolate the source of vibration.

It should be understand that, the architecture shown in FIG. 10c formeasuring wafer geometries including a wafer shape and a thicknessvariation (also referred to as wafer flatness or wafer plainness) is notlimited to the use of Fizeau interferometer, and another interferometersuch as a shearing interferometer may also be configured in thearchitecture of the present application provided with a reflectiveair-bearing chuck.

A method of determining an optimal angle at which one or more of a laserand a position sensor is located is disclosed. Referring to FIG. 10d ,to obtain an optimal Z-axis resolution, a position sensor 1026 may belocated at a position and a size of the position sensor is allowed and amaximum angle β is formed with the calibration wafer 1011. If Δh is aZ-axis resolution (or z-sensitivity), the angle β is dominant. Theformula is as follows.

Δh = Δ L × Cos β/(2Cos α)

Where ΔL is a minimum displacement detectable by the position sensor1026. The position sensor 1026 may be a commercially available sensor,for example, the minimum displacement of the sensor may be about 0.75μm.

Δh = ΔL/M Where  M = [Cos β/(2Cos (α))]^(⩓) − 1

Due to a grazing angle α incidence, Cos(α) is approximately equal to 1,and α is an angle between a light source (e.g., a laser), and thecalibration wafer 1011, and values of a generally is set as 10 degreesto 15 degrees. As β increases, M also increases based on the aboveformula, which means that the sensitivity of the position sensor 1026also increases. However, β may not be too large due to a potentialenlarging effect on a size of a spot on a detector in the positionsensor 1026 (e.g., the size of the spot have a size lager than what thedetector can detect). There may also be physical limitations about howfar the position sensor may be disposed in the device. For example, atthis grazing angle, the size of the spot of the laser on a sensorsurface may be increased by 1/Sin(90°−β)=1/Sin 30°. Table 1 below listsvarious PSD resolutions (in nm) obtained based on different values of αand β.

TABLE 1 α (°) 10.00 0.0175 10.00 10.00 β (°) 0.00 45.00 60.00 75.00 Mag(M) 1.97 2.79 3.94 7.61 PSD Res 250.000 126.93 89.75 63.46 32.85 (nm)

As shown in FIG. 10e , to calibrate the position sensor 1026, thecalibration wafer 1011 may be adjusted up and down at various positions.In this example, although each wafer is slightly different, thethickness TO of the calibration wafer 1011 may be set to 725 μm. Thethickness of the calibration wafer 1011 may be measured by a CoordinateMeasuring Machine (CMM) or another thickness measuring tool. Thecalibration wafer 1011 has a zero floating height when being located ata position 188. The position 188 may be a position of the calibrationwafer 1011 located when the calibration wafer 1011 is placed on anair-bearing chuck or vacuumed onto the air-bearing chuck, and acapacitive sensor reading obtained when the calibration wafer 1011 islocated at position 188 is denoted by CP0. CP0 may be obtained bysetting CPn to 0. Then the position sensor reading (V0 (±10V)) may beobtained from the position sensor 1026. Thereafter, the pressure or boththe vacuum and pressure may be regulated to hold the calibration wafer1011 at a position 190. A capacitive sensor reading obtained at theposition 190 is CP1, and CP1 minus CP0 equals to 20 μm (or approximatelyequals to 20 μm). A position sensor reading V1 obtained when CP1 minusCP0 is equal to 20 μm is recorded.

Thereafter, the pressure or both the vacuum and pressure may beregulated again until the calibration wafer 1011 is held at a position192. A capacitive sensor reading obtained at the position 192 is CP2,and CP2 minus CP0 approximately equals to 30 μm. A position sensorreading V2 obtained when CP2 minus CP0 is equal to 30 μm is recorded.The above steps may be repeated, and isochronal differences 40 μm, 50μm, and 60 μm are obtained when the capacitive sensor readings are CP3,CP4, and CP5, respectively.

Next, Δ(CPn−CP0) may be calculated, such as CP1−CP0, and CP2−CP0. Table2 shows the calculated exemplary results.

TABLE 2 0 1 2 3 4 5 Capacitive CP0 = CP1 = CP2 = CP3 = CP4 = CP5 =sensor 500 520 530 540 550 560 reading CPn (μm) Δ (CPn − 0 20 30 40 5060 CP0) = hx PSD V0 V1 V2 V3 V4 V5 position voltage

With the above data, hx vs Vx may be plotted, and linear fitted toobtain the slope S (μm/V) (referring to FIG. 10f ). hx is a differencebetween the capacitive sensor reading CPn and a reference capacitivesensor reading CP0, namely, a relative height of a wafer surface.Calibration data include: (1) slope: S (μm/V); (2) wafer thickness:T0=725 μm; (3) reference PSD reading: V0; and (4) reference capacitivesensor reading: CP0. The calibration data may be saved, and a softwareimplementation of the calibration may be performed by using thefollowing formula:

T_(Wafer) = T0 + (CP0 − CPn) + S × (Vx − V0).

CPn is a capacitive sensor reading obtained when the wafer is located ata predetermined floating height.

CP0 is a capacitive sensor reading obtained when the wafer is placed onan air-bearing chuck or vacuumed onto the air-bearing chuck.

Vx is a position sensor reading, in Volt.

The capacitive sensor reading in μm may be calculated from a plantcalibration constant C, C=Δh/ΔV, (μm/volt). The capacitive sensorreading CPn in μm is obtained according to the formula: CPn=C×ΔVcp.

An exemplary method of measuring a wafer shape and thickness byutilizing the architecture 1000 shown in FIG. 1c is provided in detailbelow with reference to FIG. 11 a, FIG. 11 b, FIG. 12 a, and FIG. 12 b.

There are many advantages to a measuring method of a wafer geometryperformed by utilizing an air-floating chuck and a singleinterferometer. For example, the air-bearing chuck may provide effectiveair damping capability to a wafer disposed above the air-bearing chuck.The air damping capability not only makes measurement of aninterferometer more accurate, but also helps to reduce the cost due tothe absence of expensive active vibration isolation systems and heavyacoustic isolation vibrators. Due to simplification of the wafer loadingprocess, the air damping capability also reduces the cost of wafertransfer within the architecture, for example, horizontally loading thewafer under a single interferometer. Compared to a dual Fizeauinterferometer architecture, the single interferometer architecturereduces cost by eliminating an interferometer and related optics. Alsonot needed is the mechanism for rotating a wafer 90 degrees fromhorizontal to vertical required in the dual Fizeau interferometerarchitecture. The acoustic isolation box in the dual Fizeauinterferometer architecture is also not needed in the architecture. Inaddition, the air cushion may provide air damping capability. The wholearchitecture has very few moving parts, making it more reliable than theduel Fizeau interferometer architecture. The wafer may be loadeddirectly to the air-bearing chuck to reduce wafer transport time asrequired when a dual Fizeau interferometer-based tool is configured. Theadvantage of the WGT architecture is even greater for 300 mm or 450 mmwafers, and vibration of 300 mm or 450 mm wafers may be a major sourceof noise, making it difficult to achieve a high precision in flatnessmeasurement. For devices configured for 300 mm or 450 mm wafers, opticscomponents collimators, transmission flats, and folding mirrors are alllarge and expensive. An interferometer, a wafer vertical loading system,an acoustic isolation box, and a channel of data acquisition system areeliminated, which may significantly reduce the cost for OriginalEquipment Manufacturers (OEMs) as well as to their customers.

TTV Measuring Method

FIG. 11a and FIG. 11b are schematic diagrams of performing a measuringmethod of a wafer flatness TTV by utilizing the architecture shown inFIG. 10 c. Referring to FIG. 11 a, an optical cavity formed by atransmission flat TF 1102 and a reflective air-bearing chuck 1104 ismeasured. In other words, a distance variation between opposing surfacesof the transmission flat TF 1102 and the air-bearing chuck 1104 ismeasured. The TF 1102 may sag in the middle due to gravity. A surface ofthe air-bearing chuck 1104 may not be completely flat, as illustrated inFIG. 11a and FIG. 11 b. These imperfections need to be calibrated tomake wafer flatness measurement accurate. Cavity calibration is tomeasure a cavity thickness variation. Mathematically, the cavitythickness variation is a difference between a transmission flat surfaceS_(TF)(x, y) and a chuck surface S_(CK)(x, y):ΔS_(Cavity)=S_(TF)−S_(CK). In this step, there is no wafer on the chuck.

Referring to FIG. 11 b, after calibration, a wafer 1106 is placed on thesurface of the air-bearing chuck 1104. To measure a flatness of thewafer 1106, the wafer is kept floating up on the top of the air-bearingchuck 1104 at a small air gap (for example, 5 μm to 50 μm; for anotherexample, 5 μm to 30 μm) generated by the air-bearing chuck 1104. Atthese small air gaps, the air-bearing chuck 1104 is designed to havegreat suction force, to keep a back surface of the wafer 1106 flat ormake the back surface (S_(Back surface)) of the wafer 1106 match thesurface (S_(CK)) of the air-bearing chuck 1104. In this case, locationinformation of a front surface (S_(Front surface)) of the wafer 1106 isa sum of location information of the surface S_(CK) of the air-bearingchuck 1104 and a total thickness variation TTV of the wafer 1106, thatis, S_(Front surface)=S_(CK)+TTV. The front surface of the wafer mayalso be referred to as a top surface of the wafer. However, the backsurface of the wafer is not completely matched with the surface S_(CK)of the air-bearing chuck. In actual application, to accurately determinethe location information of the front surface S_(Front surface) of thewafer, a nonconforming item (S_(N.C.)) needs to be added:S_(Front surface)=(S_(CK)+TTV+S_(N.C.)).

During measurement by utilizing an interferometer, a distance betweenthe wafer 1106 and the transmission flat may be measured:ΔS_(WFR)=(S_(TF)−S_(Front surface))=(S_(TF)−S_(CK)−TTV−S_(N.C.)).

Next, TTV may be calculated by measuring a difference(ΔS_(Cavity)−ΔS_(WFR)) between the cavity and a surface of the wafer.Subsequently, the total thickness variation may be calculated by usingthe following formula: TTV_(actual)=(ΔS_(Cavity)−ΔS_(WFR)−S_(N.C.)), andΔS_(Cavity) and ΔS_(WFR) may be measured by utilizing the interferometerin the WGT architecture shown in FIG. 10 c. S_(N.C.) may be obtainedthrough calibration. If necessary, a wafer thickness may be measured,and information about the wafer thickness is further configured tocorrect the nonconforming item. S_(N.C.) may be obtained by utilizing awafer with a known TTV (such as a double-side polished 200 mm wafer):S_(N.C.)=(ΔS_(cavity)−ΔS_(WFR)−TTV_(known)).

S_(N.C.) may drift over time, and needs to be calibrated from time totime by utilizing the wafer with the known TTV. S_(N.C.) is a functionof a wafer thickness, a temperature, a floating height FH, and a chuckflatness. All these parameters may be measured simultaneously withinterferometer data, or may be configured also for correction.

In addition, a double-side polished wafer, such as some 200 mm or 300 mmwafers, may be inverted and measured upward to obtain a shape of a backsurface of the wafer. A TTV of the wafer is then obtained in combinationwith the shape of the back surface of the wafer, a shape of the frontsurface of the wafer, and a thickness result measured by a thicknessgauge.

Shape Measuring Method

FIG. 12a and FIG. 12b are schematic diagrams of performing a measuringmethod of a wafer shape by utilizing the architecture shown in FIG. 10c. Referring to FIG. 12 a, to measure the wafer shape, a reference TF1202 (TF-ref) is first placed on a top surface of an air-bearing chuck1204 to calibrate a TF 1200 in an apparatus based on the followingformula: Cal=S_(TF)−S_(TF-ref). A flatness of the reference TF (in nm)may be much higher than the flatness of the wafer (in μm). Therefore,S_(TF-ref) is a translation term that may be removed. If TF 1200 isthick and there is minimum TF sag, the cavity calibration step may beskipped as well. In this step, there is no wafer on the chuck. Thiscalibration may be completed before delivery. Assuming that a TF shapedoes not change, tilt correction may be done at measurement time.

Referring to FIG. 12 b, in a next step, a wafer 1206 is placed on thetop surface of the air-bearing chuck 1204. To measure the wafer shape,the wafer 1206 is held at a relatively large air gap (for example, 60 μmto 1500 μm; for another example, 60 μm to 300 μm). The air-bearing chuckis designed and operated in such a way that a pressure can balance thegravity, so that there is no additional force that deforms the wafer.Therefore, at these relatively large air gaps, the wafer 1206 maintainsits natural shape while being supported by an air cushion.

SWFR = (S_(TF) − S_(Front  surface))

Next, based on an obtained difference between Cal and a measured valueof the front surface of the wafer, the wafer shape is calculated asfollows:

Wafer  shape = Cal − SWFR = (S_(TF) − S_(Tf-ref)) − (S_(TF) − S_(Front  surface)) = S_(Front  surface) − S_(TF-ref) = S_(Front  surface).

Since the reference TF has a relatively high flatness, S_(TF-ref) may beequivalent to a constant. Both S_(Front surface)−S_(TF-ref) andS_(Front surface) may be configured to reflect the wafer shape, namely,the shape of the front surface of the wafer. Shape measurement performedaccording to the above steps is accurate, and does not need correctionso long as the air gap is set properly. This could be an ideal toolarchitecture for a patterned wafer geometry (Patterned Wafer Geometry,PWG) tool. In addition, the architecture of the present application hasbetter precision, matching, and lower cost than the dual Fizeauinterferometer architecture. In this architecture, a grating-basedshearing interferometer may be configured to replace the Fizeauinterferometer, and the air-bearing chuck may be configured to replacethree lift pins for support, thereby improving measurement accuracy ofthe shearing interferometer and increasing the measured warp dynamicrange by tilting the wafer.

For a wafer with a relatively large warp, a 2-D tilt platform may beconfigured to overcome limitations to a dynamic range of theinterferometer in the architecture shown in FIG. 10c . When the wafer istilted, a shape of the wafer 1306 in a horizontal position may be bettermaintained than a same wafer 1306′ in the vertical position. As shown inFIG. 13, when the same wafer 1306′ is in the vertical position, if thewafer 1306′ is not completely vertical, the shape of the wafer 1306′ maybe changed by gravity.

Specifically, FIG. 13 illustrates that the wafer 1306′ in a verticalposition is prone to shape change when tilted. This is because when thevertically clamped wafer 1306′ is tilted, a torque T is applied to thewafer 1306′. The torque will change the shape of the wafer. Measurementaccuracy of a traditional dual Fizeau interferometer is affected. Incomparison, the architecture disclosed in the present applicationsupports the wafer 1306 on a thin air cushion that helps maintain anatural shape of the wafer 1306 even when the wafer 1306 is at arelatively small tilt angle (usually less than a fraction of onedegree), as shown in the horizontal setting of FIG. 13.

The architecture disclosed in the present application may be configuredto measure a warp of a thin wafer. When the wafer is tilted in thevertical position, the wafer is too thin to be put in the verticalposition or too thin to keep its shape unchanged. For some thin wafers,it may be too thin to form a support at two points on the edge of thewafer. In this architecture, the wafer is in the horizontal position andsupported by the air cushion. When the wafer is tilted, a very smallradial force is applied to the wafer to maintain the position of thewafer. At proper floating height, vacuum setting and pressure setting,the warp of a thin wafer may be measured.

Accordingly, a wafer geometry tool and a patterned wafer geometry toolthat use the above method may have high precision and high throughput,but at about half price as compared with the dual Fizeau interferometerarchitecture. This method provides a cost-effective and high precisionsolution for wafer flatness, nano-topography, and shape measurementtools for wafers of any size such as 200 mm, 300 mm, and 450 mm.

FIG. 14 is a schematic structural diagram of an exemplary goniometer1400 for measuring a patterned wafer tilt platform according to anembodiment of the present application. The steps in the presentapplication include two stacked goniometers 1400 that are utilized toincrease a warp dynamic range of a wafer and throughput. When the waferis tilted, the wafer may be maintained to be focused. It should be notedthat, an X platform 1402 and a Y platform 1404 intersect at an angle of90 degrees. In FIG. 14, the X platform 1402 and the Y platform 1404 aredrawn on a same plane to facilitate illustration of a common rotationcenter.

Method for Differentiating Between a Real Feature and a Chuck Mark (orArtifact) on a Surface Wafer

The embodiment of the architecture 1000 shown in FIG. 10c may implementan artifact-free measurement. In the architecture 1000, the wafer 1014may be loaded to measurement chamber directly from handler end effector.

In the embodiment of the WGT architecture 1000 shown in FIG. 10 c, atotal thickness variation and a wafer shape are measured by utilizing avertically mounted Fizeau interferometer. However, in actualapplication, this method has many challenges. An air-bearing chuckitself may not be flat and there may be artifacts, such as particles, ona top surface of the air-bearing chuck. When a wafer is vacuumed on theair-bearing chuck, the artifacts may show up on a top surface of thewafer. For example, FIG. 15a illustrates an example in which a chuckmark or artifact occurred when a wafer is vacuum down on a chuck. Alarge particle 1502 may appear as a bulge on a wafer 1504 a on a topside of an air-bearing chuck 1500 a, as illustrated in FIG. 15 a. Thesetypes of artifacts may be calibrated by utilizing a method disclosed inthe present application. FIG. 15b is a schematic diagram of a wafer 1504b floating up on an air-bearing chuck 1500 b, where no chuck marks andartifacts are found on the wafer 1504 b.

FIG. 16a to FIG. 16c are schematic diagrams of a method fordifferentiating between real features 1604 and chuck marks (orartifacts) 1606 on a wafer surface 1610. FIG. 16a is a schematic diagramof wafer geometry measurement on a surface S1. The real features 1604are mixed with the chuck marks (or artifacts) 1606 during measurement ofthe interferometer. FIG. 16b is a schematic diagram of wafer geometrymeasurement on a surface S2. The surface S2 is a chuck surface obtainedby rotating a chuck 180 degrees from an original location where themeasurement on the surface S1 is performed. When the chuck marks (orartifacts) 1606 rotate 180 degrees with a chuck 1600, the real features1604 remain in the same location. Thus, the wafer 1610 is placed on thechuck surface S2 (as shown in FIG. 16b ) obtained after the rotation by180 degrees, and a measurement result obtained when the wafer 1610 is onthe surface S2 is compared with a measurement result obtained when thewafer 1610 is on the surface S1 of 0 degrees (as shown in FIG. 16a ), sothat real features 1604 (those remain in the same location in the wafercoordinate system before and after the rotation) of the wafer 1610 maybe identified. On the contrary, when the wafer 1610 is rotated 180degrees, a location of the chuck marks (or artifacts) 1606 is off by 180degrees in the wafer coordinate system.

FIG. 16c provides a S1 and S2 difference map showing a pair of chuckartifacts 1616 and 1620. These chuck artifacts may be calibrated if theydo not move around on the chuck. These chuck artifacts also havespecific features that allow them to be removed by utilizing analgorithm if the chuck is clean and the chuck artifacts are isolated.When there are limited artifacts on any one or more of a top surface ofthe chuck and a back surface of the wafer, a wafer or chuck rotationmethod may be configured to identify these artifacts and remove them.

Although the embodiments of the present application have been fullydescribed with reference to the accompanying drawings, it should benoted that, various changes and modifications will become apparent tothose skilled in the art. Such changes and modifications should beunderstood to be included in the scope of the embodiments of the presentapplication defined by the appended claims.

What is claimed is:
 1. An air-bearing chuck, comprising: a nozzleportion, provided with a plurality of support force nozzles forgenerating an air cushion on a top surface of the nozzle portion; and agas channel portion, comprising a first gas channel configured totransmit a first gas to the plurality of support force nozzles toprovide support force.
 2. The air-bearing chuck according to claim 1,wherein the nozzle portion further comprises a plurality of openings,and the plurality of openings are arranged alternately with theplurality of support force nozzles.
 3. The air-bearing chuck accordingto claim 2, wherein the plurality of support force nozzles and theplurality of openings are arranged in an axisymmetric pattern on the topsurface of the nozzle portion.
 4. The air-bearing chuck according toclaim 2, wherein the plurality of support force nozzles and theplurality of openings are arranged in a plurality of concentric nozzlerings equally spaced at an interval of ΔR.
 5. The air-bearing chuckaccording to claim 4, wherein a radius of a nozzle ring, farthest fromthe center of the air-bearing chuck, of the plurality of concentricnozzle rings is 0 mm-20 mm smaller than a radius of the air-bearingchuck.
 6. The air-bearing chuck according to claim 4, wherein eachsupport force nozzle and an adjacent opening that are on any one of theplurality of concentric nozzle rings are tangentially spaced at aconstant distance ΔT.
 7. The air-bearing chuck according to claim 6,wherein as a distance between per nozzle ring of the plurality ofconcentric nozzle rings and the center of the air-bearing chuckincreases, a total number of nozzles on per nozzle ring increases in aneven number, and the even number comprises any one of 2, 4, 6, 8 and 10.8. The air-bearing chuck according to claim 6, wherein a differencebetween ΔR and ΔT is less than 5 mm.
 9. The air-bearing chuck accordingto claim 2, wherein the plurality of openings comprise a plurality ofsuction force nozzles, the gas channel portion further comprises asecond gas channel, and the second gas channel is configured to transmita second gas to the plurality of suction force nozzles to providesuction force.
 10. The air-bearing chuck according to claim 9, wherein aplurality of first gas through holes corresponding to the plurality ofsupport force nozzles are disposed on both the nozzle portion and thegas channel portion, and a plurality of second gas through holescorresponding to the plurality of openings are disposed on both thenozzle portion and the gas channel portion, the first gas channel isconnected to the plurality of support force nozzles through theplurality of first gas through holes, and the second gas channel isconnected to the plurality of openings through the plurality of secondgas through holes.
 11. The air-bearing chuck according to claim 9,wherein the first gas channel comprises a first annular channel and aplurality of first channels connected to the first annular channel, andthe second gas channel comprises a second annular channel and aplurality of second channels connected to the second annular channel.12. The air-bearing chuck according to claim 9, wherein the gas channelportion comprises a first gas layer and a second gas layer that arestacked, the first gas channel is located in the first gas layer, andthe second gas channel is located in the second gas layer.
 13. Theair-bearing chuck according to claim 12, wherein the first gas layer isprovided with a first groove for accommodating the first gas channel,and the second gas layer is provided with a second groove foraccommodating the second gas channel.
 14. The air-bearing chuckaccording to claim 9, further comprising: an air pressure regulator,configured to regulate a flow rate of a gas in each of the first gaschannel and the second gas channel to hold a wafer at a predetermineddistance from the top surface of the nozzle portion, so as to measure ageometry of the wafer, wherein the geometry of the wafer comprises oneor more of a flatness and a shape of the wafer.
 15. The air-bearingchuck according to claim 14, further comprising: a controller,configured to control the air pressure regulator to regulate the flowrate of the gas in each of the first gas channel and the second gaschannel to hold the wafer at the predetermined distance from the topsurface of the nozzle portion, so as to measure the geometry of thewafer.
 16. The air-bearing chuck according to claim 15, wherein thepredetermined distance ranges from 0 μm to 50 μm when the air-bearingchuck is configured to measure the flatness of the wafer.
 17. Theair-bearing chuck according to claim 15, wherein the predetermineddistance ranges from 60 μm to 1500 μm when the air-bearing chuck isconfigured to measure the shape of the wafer.
 18. The air-bearing chuckaccording to claim 2, wherein the plurality of openings comprise aplurality of flow guide holes, the plurality of flow guide holes areconfigured to guide the first gas ejected from the plurality of supportforce nozzles to flow back to the nozzle portion when the first gasencounters the wafer, the gas channel portion further comprises a thirdgas channel, and the third gas channel is configured to make the firstgas that has flowed back to the nozzle portion flow out of theair-bearing chuck.
 19. The air-bearing chuck according to claim 1,wherein the air-bearing chuck has a mirror polished surface higher thanor equal to level N4 in accordance with an ISO standard.
 20. Theair-bearing chuck according to claim 1, wherein a material of the nozzleportion comprises any one of aluminum, glass, microcrystalline siliconand ceramic, the material is mirror polished, and the top surface,obtained after being polished, of the nozzle portion is sufficientlyflat, so that interference fringes are shown on the top surface of thenozzle portion.